Recent immunocytochemistry has revealed a rich distribution of several neuropeptide projections throughout the brain. The new information raises two major problems: 1) What is the function of these "extrahypothalamic" projections. 2) What is the chemical nature of an antigen detected immunocytochemically by a given antiserum in an unexpected location. Two model systems will be used in trying to answer these queries. For the first query, we will trace extrahypothalamic vasopressin fibers in 100 microns thick immunocytochemically stained sections to yield Golgi-like immunospecific images. We will try to differentiate axons and dendrites morphologically and functionally. For the second query, we will endeavor to develop a procedure for obtaining specific antibody to a substance which has not yet been isolated in pure form. This will be done by selection specific antibody-producing clones in mixtures of immune cell-myeloma hybridomas grown in vitro, using immunocytochemical criteria rather than methods that require purified antigens. Antibodies so selected may, in a scope beyond the present proposal, be used for identifying and sequencing new antigens without need for elaborate isolation or purification. As a model for this approach, we will use, in the present proposal, pineal factor, a still unpurified, nonmelatonin antagonist to LHRH, that is immunologically cross-reactive with LHRH. We will attempt to select hybridoma cells that produce monoclonal antibody specific for the pineal peptide but lacking cross-reactivity with LHRH.